breathalyzers arent 100% accurate though (for example if you drink certain mouthwash immediately before a breathalyzer test it gives a false positive) so it's not allowed as evidence in courts. I think they can use a breathalyzer as suspicion enough to arrest, but they have to prove through other means for a conviction.

what shaung said, here in canada, over the breathalyzer limit will send you to jail.if positive you need to give a blood sample. i've seen people who are absolutely wasted but you would never suspect they are drunk.